I have a USB powered LED curtain which is attached to a smart plug so I can set it to come on at certain times etc. The trouble is there are multiple "modes" (flashing, alternating etc.) which i'm not interested in but it won't stay set to always on and I have no use for the other modes.

My plan is to bypass the circuit board containing the chip, IR receiver, mode button etc by soldering the lights directly to a new USB connector so the lights are just constantly on when the smart plug is on.

The trouble i'm having is determining some of the values necessary to work out what resistor I would need to use. I have a ton of different resistors and a multimeter and I have done some reading on working out values for LEDs but none seem to refer to these really thin string light curtain type things which is where the confusion comes in.

Here are the values I have from the product specs:

Known Values

I'm happy to experiment a little but since i'm basically a newbie i'm wary that I don't want to blow the lights or create any potential fire hazards.

Is someone able to quickly run me through what I need to measure/work out in order to determine the resistance needed please? I haven't done anything other than remove the circuit board cover so i'm able to take measurements while they are plugged in if that's any help.

Thanks in advance!

  • \$\begingroup\$ why don't you think they refer to these really thin string light curtain type things? I bet these really thin string light curtain type things are just LEDs and wires and some plastic to make them look pretty. There might be resistors inside already. There probably are, if the output is 5V \$\endgroup\$
    – user253751
    Dec 1, 2020 at 13:01
  • \$\begingroup\$ A) If you can measure the actual current that would be best. However, the current may be be rapidly pulsed, so be careful about that. You want the average value. B) LED brightness is directly relatated to current. You could compare the brightness with known LEDs to guess their current rating. C) You could start off with a large value resistor, observe the brightness, and gradually reduce resistor values, until the LEDs seem their normal brightness. It would be helpful to have an unmodified string on hand to compare with. \$\endgroup\$ Dec 1, 2020 at 13:10
  • \$\begingroup\$ To be honest it's just because they tend to refer to a single standard size LED with values based on the colour. There are over 300 extra tiny ones here arranged in a curtain pattern which brings all sorts of variables that I'm not knowledgeable enough to know whether they matter or not. Maybe it does apply and I have to figure it out but i'm just not sure. \$\endgroup\$ Dec 1, 2020 at 13:10
  • \$\begingroup\$ @MathKeepsMeBusy Thankyou, I did consider running a large value resistor and working my way down. I have a breadboard which should make that quite easy. If I get them roughly to the same brightness would that be considered safe without any extra calculations? Also what would be considered a high value to start with in this context? \$\endgroup\$ Dec 1, 2020 at 13:15

1 Answer 1


Am just a beginner but I think the best way to start your plan is to measure the voltage output of adaptor with the LEDs switched off or disconnected. After you measure that check the input of your LEDs, if there is no label then you can check them one by one using a cellphone charger or 5v dc adaptor. Use the positive and negative wire to determine how much brightness it can produce with 5v dc, and it can also determine if that LED is working. And also 5v is not that powerful enough to overload the current through led so I think it is safe. After you measure/check every LEDs, you can sum them up (5 LEDs = 10DCV) then start a way of using components to make a suitable power output for your LEDs, but I suggest to you is just buy an adaptor(laptop adaptor) with at least 24v (to power up all your LEDs).

  • \$\begingroup\$ please don't directly connect LEDs to a 5V voltage source. \$\endgroup\$ May 6, 2021 at 15:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.